1. Field of the Invention
The present invention relates to the field of orthopedic surgery and in particular to making incisions in the skin and soft tissues to go directly to the surface of a fractured bone to affix locking screws into the bone. The present invention further relates to the use of a locking nail and guide means to reach to the surface of the bone so that a proper incision can be made to enable a locking screw to be affixed into the bone and the embedded locking nail with a minimum of surgical cutting and blood loss. The present invention also relates to the field of scalpels used to make the required incision so that a locking screw can be affixed into the bone with a minimum of surgical cutting and blood loss.
2. Description of the Prior Art
The fairly recent development of intra-medullary locking nails has been a significant breakthrough in the surgical management of fractures of the long bones in humans and animals.
Locking nails provide superior fixation to that provided by on-lay plates secured by screws. Equally significantly, they can be installed in the bone with far less surgical injury to the patient. The skin incisions are smaller. The soft-tissue trauma is less. The amount of blood-loss is much less. The overall recovery from surgery is speedier and more pain-free. The impact of locking nails on the surgical management of long-bone fractures cannot be overstated.
The installation of a locking nail, which is a long metal rod and will be interchangeably referred to as a rod or a nail, is accomplished by inserting it, through a small skin incision, into one end of the bone, and advancing it into the bone cavity (medullary cavity) so that the rod is embedded within that cavity. This metal rod has preformed holes at intervals along its length for receiving screws that are inserted transversely or obliquely through the shaft of the bone. In this way the traversing screws lock the bone fragments to the embedded rod, or conversely, lock the rod to the bone. Each traversing screw is inserted into the bone through a small skin incision, and herein lays the problem.
For the placement of each traversing screw, the technical problems for the surgeon include, firstly, making the small skin incision at the correct location and correct angle on the skin surface, and extending the incision through the skin and soft-tissues, down to the bone surface. Instruments are now passed through this small skin and soft-tissue path, to drill a hole that passes through one side of the bone, through the unseen hole in the rod, and into the bone on the far side of the rod.
The challenge of finding the exact spot on the bone's outer surface to drill the first hole, and then to drill in precisely the right direction for the drill bit to pass centrally through the hole in the rod, has been ingeniously solved by the use of a targeting guide. The targeting guide is attached to an outrigger that is rigidly, and removably, attached to one end of the rod. When the nail is embedded in the bone, this attached outrigger and targeting guide protrude from the insertion wound, and lie outside the body. Note that in some device brands, the outrigger and targeting device are a single part. The targeting guide lies parallel with the embedded nail. Within the targeting guide, along its shaft, are tunnels (the targeting guide tunnels) that line up precisely with the holes in the embedded, and unseen, rod. In placing a screw through the bone and the hole in the embedded rod, various instruments are passed through the matching targeting guide tunnel in the targeting guide. Drill bits are long and narrow and sometimes brittle, and their rotating motion can damage soft-tissues. For this reason they are supported and guided, and the tissues are protected from them, by passing them through a metal sheath, the drill-guide. There is no standard nomenclature in the industry for the terms “outrigger”, “targeting guide” and “targeting guide tunnel”, but the usage of these terms in this patent application can leave no doubt as to the meaning of these terms as used here.
The drill guide is a metal tube that has an outer diameter such that it snugly passes through the matching targeting guide tunnel. The inner diameter of the drill guide is such that the drill bit snugly passes through it. Its leading edge cones down to a bullet-nose.
As a first step for inserting a screw through the wall of the bone and into the underlying rod-hole, the drill-guide is inserted into the matching targeting guide tunnel. The drill guide is advanced to the skin. A mark is made at the site of skin contact. The drill guide is withdrawn, and an incision is made through the skin and soft-tissues until the scalpel blade reaches the bone.
The drill guide is now advanced through this skin incision and soft-tissue path, until its advancing end comes into contact with the bone. The drill-guide, thus placed, is now perfectly located to guide a drill bit to the correct site on the surface of the bone, at precisely the correct angle, to drill through the bone and through the hole in the rod. The drill bit is then advanced deeper into the bone, or out through the opposite cortex (wall) of the bone. Once a hole has been drilled through the bone and the hole in the rod, the drill guide is removed from the targeting guide tunnel and a screw guide sleeve is inserted into the targeting guide tunnel. The screw guide sleeve is used to guide the screw and the screwdriver to the nearside hole in the bone, and through it to the hole in the nail, and out through the hole into the bone on the other side of the nail.
The current practice for cutting the skin incision and a path through the soft-tissues down to the bone is crude and imprecise. The current practice starts wherein the skin entry-site is located by advancing the drill guide through its targeting guide tunnel until it touches the skin. A mark then is made on the skin at the contact site. The drill guide is partly withdrawn away from the skin but is left in the targeting guide tunnel. The surgeon then makes a free-hand skin incision at the marked skin site, using a regular, standard, single-bladed scalpel. The bulky targeting guide blocks direct access to the skin and the surgeon has to work around it. The only direct access to the marked skin site would be though a targeting guide tunnel. As things currently stand, the scalpel is now directed in front of or behind the targeting guide, angled obliquely through the skin incision and soft-tissues, at an approximately anticipated compensating angle, to a mentally calculated and imprecise location on the bone surface. Because this is not the best angle for the incision, the surgeon makes an oversized, irregular skin cut and soft-tissue path that is not at an ideal angle.
For the scalpel to make the skin incision and soft-tissue path at the correct angle and with the shortest path from the skin to the bone would require that the scalpel pass directly though the targeting guide tunnel. Since the targeting guide tunnel guides the drill guide to the precise location on the bone for drilling the hole into the bone, the same tunnel could usefully serve to accurately guide a scalpel through the skin and soft-tissues to the same, precise target point on the bone.
One problem with this solution is that commercially available scalpels do not have handles that are long enough to pass through the targeting guide tunnel and cover the distance down to the bone. If the a scalpel had a longer handle, the surgeon could make a straight pass with the blade, directly through the targeting guide tunnel, through the skin and soft tissues, and down to the bone.
The above solution by itself is not presently viable because an incision made through the targeting guide tunnel with the currently available fixed-blade scalpels would be too small to accommodate the drill guide or the screw driver sleeve. This is because the widest blade that could pass through the targeting guide tunnel would have a width equal to the internal diameter of the targeting guide tunnel. However, a skin incision whose length equals the internal diameter of the targeting guide tunnel would be insufficient to allow passage of a cylindrical instrument (such as the drill guide) that has an external diameter that equals the internal diameter the targeting guide tunnel. If the skin had no elasticity, the length of the smallest skin incision that will allow passage of the drill guide can be calculated; it is equal to half the circumference of the drill guide. The circumference (C) of the cylindrical drill guide is calculated as π multiplied by the diameter (D) of the drill guide (C=πD). Thus, if the diameter of drill guide were 10 mm, the circumference of the drill guide would be 3.14 multiplied by 10 mm, which equals a circumference of 31.4 mm. In non-elastic skin the length (LI) of the smallest skin incision that would accommodate the drill guide would therefore be half the circumference (C) of the drill guide. LI=πD×0.5. Thus, in non-elastic skin, a skin incision 15.7 mm long is needed for a 10 mm cylindrical drill guide to pass through it: i.e. an incision that is 57% longer than the diameter of the cylindrical drill guide. It can be seen that at present, the widest scalpel blade that could pass through a 10 mm diameter targeting guide tunnel, cannot be 15.7 mm wide, but instead only 10 mm wide, and further, that a 10 mm rigidly guided scalpel blade cannot make an incision that is greater than 10 mm wide, such as the 15.7 mm that is needed in the present example, if the scalpel cuts only in a thrusting mode, with no side to side slicing motion. This percentage is constant: in non-elastic skin, the incision needed for passage of a cylindrical instrument will need to be 57% longer than the diameter of that instrument for all sizes of instrument.
Human skin does have elasticity, and normally, an incision in human skin will stretch 25% to 30%. This is still less than the 57% needed for a cylindrical instrument to pass through a skin incision that equals in length the diameter of that cylindrical instrument.
Therefore, even allowing for the elasticity of normal human skin, the widest, fixed-blade scalpel blade that could be passed through any size targeting guide tunnel could not make a skin incision adequate for the passage of the corresponding drill guide.
Given the elasticity of human skin, the present invention scalpel instruments can make an incision that is less than the 57% enlargement, and still be adequate.
Assuming a skin stretch of 25%, a 12.6 mm incision will stretch to 15.75 mm, which is sufficient for the passage of a 10 mm cylindrical instrument. This is 2.6 mm (26%) greater than the drill guide diameter of 10 mm.
In summary, assuming a skin incision that will stretch 25%, the incision will need to be 26% longer than the diameter of any cylindrical instrument, to enable the said instrument to pass through that incision.
Locking screws placed through the lateral aspect of the proximal femur have to pass through a tough, inelastic fascial layer, called the fascia lata. The fascia lata poses a special problem over the proximal femur in locking nail fracture fixation. The iliotibial band is not quite as thick or tough as the fascia lata, but it poses a similar problem over the lateral aspect of the distal femur. The term “deep fascia” will be used to describe either. The deep fascia forms a barrier to the passage of the drill guide and other instruments. It lies against the bone at the deepest part of the narrow soft tissue incision tunnel. A pointed knife thrust straight into it will only make a small puncture hole. Slicing motion is required to adequately enlarge the puncture hole for passage of the instruments. It is impossible to enlarge the puncture hole without enlarging the soft tissue tunnel as well, thereby causing additional soft tissue damage.
In current practice, the surgeon passes the scalpel anterior or posterior to the targeting guide and through the skin and soft tissues, to blindly slice the deep fascia. Made in this oblique fashion, the fascial incision does not line up perfectly with a straight line between the targeting guide tunnel and the target point on the bone surface. The surgeon therefore makes long sweeping motions with the tip of the knife, making an unnecessarily oversized fascial incision. The fascial incision cannot be repaired later, since it lies in the depth of a narrow soft-tissue tunnel. The fascia lata connects to the iliotibial band. Both play a vital role in normal gait. Excessive damage to the fascia lata or iliotibial Band may later result in impaired gait.
There are many “perforating” arteries just deep to the fascia lata. The larger the fascial incision the more blood vessels will be cut, causing proportionately increased bleeding.
A tunnel-guided-knife as described herein will predictably make the smallest possible skin and soft tissue incision. However, a sharp-pointed blade plunged through the skin straight down to the bone, and then withdrawn back along the identical path, guided in and out by the rigid targeting guide tunnel, will have a terminal configuration that strictly matches the profile of the blade.
Any blade, other than a chisel-shaped blade, will always have a sharp-pointed leading edge, which will cause the terminal end of the tunnel to be triangular. A chisel-blade is impractical since it will not penetrate the skin. A triangular end-tunnel will be of no consequence where the entire tunnel is through soft tissues, such as fat and muscle. However, the deep facia along the lateral thigh is a tough barrier that lies adjacent to the bone.
Any in-and-out blade, other than a chisel, will penetrate the deep fascia with an incision that is always less than the full width of the blade, and likely to be little more than a puncture point. Enlarging the deep fascial incision with a pointed blade would require side-to-side slicing motion, which is not possible with a fixed blade, attached to a rigid cylindrical handle, which is guided by a rigid targeting guide tunnel. Making a minimal incision in the deep fascia at the terminal end of a minimal skin and soft tissue tunnel thus represents a special challenge in using a tunnel-guided knife.
For the sake of speed and convenience, given the technical problems of blindly passing a scalpel anterior or posterior to the targeting guide, surgeons frequently make an initial skin incision, soft-tissue path and fascial incision that is much larger than the minimum needed to get the job done. Alternatively, the surgeon may start with a small, tentative skin incision and enlarge it when he/she finds that it is too small for the drill guide to pass through. This free hand, secondary enlargement will often result in a jagged incision, and the subsequent healed scar will be jagged and cosmetically unsatisfactory.
Additionally, skin incisions and soft-tissue tunnels must be made for each screw, and there is at least one and generally multiple screws that must be applied. At the end of the operation the surgeon has to close each of the individual skin wounds, a process which can be time-consuming, the total time being directly related to the length of each incision.
In the operation of locking nail fracture fixation, there are compelling reasons for the locking-screw incisions through the skin, soft tissues and deep fascia to be as small as possible. The smallest incisions can only be made through the targeting guide tunnel. Ideally each incision needs to be just large enough to accommodate the outer diameter of the drill guide. Skin and soft tissue incisions made through the targeting guide tunnel with a fixed-blade scalpel are too small. A pointed knife thrust straight into the deep fascia through the targeting guide tunnel will only make a small puncture hole, and slicing motion is required for an adequate incision.